A circulating press of this species is known in the art from DE-GM 88 16 064. Herein, the upper and lower stamps are adapted rotatably about their longitudinal axes, directly after passing the pressure rollers loading the latter. The rotation of the upper and lower stamps about their longitudinal axes is achieved either by a frictional connection of the upper and lower stamps with guide cam sections arranged directly behind the pressure rollers loading the upper and lower stamps and adapted to be pressed under spring action against the upper and lower stamps, or by cooperation of a serrated section provided at the shaft of the stamp with a stationarily disposed toothed rack. By the rotational movement of upper and lower stamps directly after the pressing procedure and during the extraction of the upper and lower stamps from the die of the die table, it is intended to obtain a separation of the surface of the pressed tablet at least from the upper stamp. With particularly adhering materials to be pressed, a rotational movement of the lower stamp is to avoid the adhesion between the latter and the lower side of the tablet.
It is disadvantageous, with the frictional connection between upper and lower stamps and the respective guide cam sections, however, that, hereby, on one hand, there is wear, and, on the other hand, no defined rotation of upper and lower stamps is performed. With different rotations, e.g., of upper and lower stamps, even a destruction of the pressed shaped body must be expected. With the serrated section provided at the shaft of the stamp, it is disadvantageous, on one hand, that particularly adapted upper and lower stamps have to be employed, and, on the other hand, that friction between the serrated sections of upper and lower stamps and the respective stationary toothed racks will occur, since the serrated section of the upper and lower stamps will be moved, together with the latter, in axial direction of the upper and lower stamps. It is disadvantageous, further, that, with the engagement of the serrated sections into the respective, stationarily arranged toothed rack, jamming may occur, depending on in which position the respective upper or lower stamp has remained after leaving the respective toothed rack. In total, with this prior art circulating press, there is the disadvantage that the rotation of the upper and lower stamps is achieved only after passing the pressure rollers loading the latter. This is disadvantageous in that the pressed shaped bodies will adhere already, before a rotational movement takes place.
From U.S. Pat. No. 3,337,915, there is known a circulating press of a different species, wherein the upper and lower stamps are also rotated after passing the respective pressure rollers. The rotation is performed, here, under application of a pressure force, which is, however, smaller than the pressure force exerted by the pressure rollers. For rotating the upper and lower stamps, there are mounted thereon cams, which will run, immediately after passing the pressure rollers, against interior or exterior cam rollers causing a swinging action of the cams and thus of the upper and lower stamps under loading by a smaller pressure force. It is disadvantageous, here, that the cams running against the cam rollers will cause noise, and that the cams assigned to the individual upper and lower stamps will not allow for a variation of the angle of rotation of the upper and lower stamps, unless the individual cams of each upper and lower stamp are replaced by differently shaped cams. In an embodiment of this circulating press of a different species, the upper and lower stamps are axially movably, but non-rotatably guided in sleeves, at which cams are attached. For a variation of the angle of rotation of the upper and lower stamps, however, even the sleeves have to be replaced here, which is extremely time-consuming.
Further, from U.S. Pat. No. 3,118,183, there is known in the art a circulating press, also of a different species, wherein the rotation of upper and lower stamps is achieved simultaneously with the pressing procedure by loading upper and lower stamps by pressure rollers. In an embodiment thereof, friction wheels are employed for rotating the upper and lower stamps. This does not allow for a synchronous movement of upper and lower stamps, and causes, in particular under consideration of the simultaneously occurring, relative high pressure forces caused by the pressure rollers, relatively high wear. In another embodiment, cam-type members are inserted into cross slots of upper and lower stamps, which cooperate with stationarily disposed cam rollers. Here, too, in particular under consideration of the simultaneously occurring pressure forces, high wear will occur, and there will be a rattling noise within the circulating press.